This invention relates to injection molding and more particularly to fluid cooled hydraulic actuating mechanism for a multi-cavity valve gated injection molding system.
It is well known to use hydraulically actuated pistons to reciprocate the valve pins in a valve gated injection molding system. One previous arrangement is shown in U.S. Pat. No. 4,468,191 to Gellert entitled "Hydraulically Actuated Injection Molding System with Alternated Hydraulic Connections" which issued Aug. 28, 1984. Although the actuating mechanism is seated in a water cooled back plate, overheating of the mechanism is a considerable problem with these systems. This is particularly true with the increasing demand to mold high performance engineering resins such as glass filled ULTEM (trade mark) where melt temperatures are as high as 850.degree. F. During use, some heat is conducted and radiated from the heated manifold and the valve pin which results in the operating temperature gradually building up to an unacceptable level. This can lead to the hardening or material decomposition and break down of seals and O-rings, resulting in the leakage of hydraulic fluid.
In previous injection molding actuating mechanisms such as that shown in U.S. Pat. No. 4,468,191 referred to above, hydraulic fluid is connected by circumferential grooves to holes on opposite sides of the cylinder. However, there is no provision for continuous flow of hydraulic fluid and it remains static and gradually heats up. Other unsatisfactory attempts have been made to utilize flow of the hydraulic fluid for cooling, but none have produced adequate flow of fluid through the cylinder.